A number of different properties is required of a drive system for industrial trucks, specifically high ride comfort, high travel performances, and low energy consumption. It is further important for the industrial truck to exhibit high handling efficiencies and high accelerations, also in the case of a change in the direction of travel. It is further desirable for the drive to be controllable well during the transport of fragile goods. In cases where an industrial truck is operated in halls or containers the requirement is that no noxious substances be emitted.
The invention relies on a drive system which uses an internal combustion engine. The property typical of an internal combustion engine is that it has an range for power output that is limited by a minimum and a maximum speed, the internal combustion engine naturally being operated exclusively in one sense of rotation. The specific energy consumption of the internal combustion engine can be represented in the form of a family of characteristics in dependence on the speed and the torque produced. Commonly, one or more characteristic curves are established in the family of characteristics that constitute a compromise between a low-consumption operation and an acceleration reserve. Each value of the power input has associated therewith a speed of the driving machine. To achieve high travel performances at a high ride comfort and low consumption of energy, gearing systems are required which have a wide range of adjustable transmission ratios which is infinitely variable, if possible, in order to operate the internal combustion engine largely independently of the travel speed at the speed associated with the power input according to the characteristic curve.
Additional units are connected to the drive system, e.g. hydraulic pumps. Because of their construction type, they act adversely on the speed of the internal combustion engine because they apply their load abruptly, and can cause the engine to be stalled. Therefore, such additional units necessitate dynamic drive systems which can be adjusted to variations of the load at low time constants.
DE 199 55 313 has made known a drive system for industrial trucks which has an internal combustion engine, an electric motor fed from a battery, a gear assembly, and a change-speed gearing for the reversal of the sense of rotation in conjunction with the output shaft. The gear assembly has its input shafts coupled to the internal combustion engine and the electric motor. The output shaft is coupled to the output shaft of the drive system.
DE 199 55 311 A1 has made known a drive system for industrial trucks in which the shaft of an internal combustion engine is coupled to an infinitely variable shift mechanism. A gear assembly has its input shaft coupled to the shaft of the internal combustion engine and has a second input shaft coupled to the output shaft of the variable shift mechanism. An electric motor the shaft of which is coupled to a third input shaft of the gear assembly is controlled from a battery via a power electronic system. A change-speed gearing is arranged between the output shaft of the gear assembly and the driving wheels of the industrial truck. The speeds of the internal combustion engine, electric motor, and output shaft of the change-speed gearing and possibly the charging condition of the battery are measured by a sensor system. In response to set-point signals from the set-point transmitters actuated by an operator of the industrial truck and on the basis of the signals outputted by the sensor system, a regulation device regulates the speed of the electric motor and combustion engine and/or the transmission ratio of the shift mechanism and, if necessary, a rotary brake, and shifts the shift mechanism. In the drive system mentioned last, a reduction occurs to the maximum power to be transmitted by the shift mechanism. This allows to use shift mechanisms the operating efficiency of which otherwise would not be sufficient. The transmission ratio between the internal combustion engine and the output shaft of the drive system can be made zero. This allows to keep the truck at rest with the internal combustion engine running with no need to break the flow of power via a clutch. In addition, it allows to obtain a spread of any magnitude for the transmission ratio.
The invention is based on a branching of power which is performed in the known drive systems, and intends to achieve the object of further improving the travel performances at a high ride comfort and obtaining good regulability infinitely within a large range of adjustable gear ratios. In addition, the object is to achieve a rapid correction in case of an abrupt application of load by additional units and to make possible a zero-emission mode at least for a short period.